A versioned domain model demonstration.

To see how to use the versioned domain model please see the unit tests in
vdm/dm_test.py.

## Copyright and License

(c) 2007 Rufus Pollock.

Licensed under the MIT license:

  <http://www.opensource.org/licenses/mit-license.php>

## Documentation

A great starting point is Fowler's *Patters for things that change with time*:

  http://www.martinfowler.com/ap2/timeNarrative.html

In particular Temporal Object:

  http://www.martinfowler.com/ap2/temporalObject.html

In addition we make heavy use of various other standard patterns (references
are to PoEAA) such as Unit of Work.